How DNS Works: The Internets Phone Book Explained

Every time you type a website address, something happens behind the scenes that most people never think about. Your browser needs to figure out which server to connect to, and it does this using DNS - the Domain Name System.

Understanding DNS is useful whether you are a developer, run your own website, or just want to know how the internet works. This is the explanation I wish someone had given me years ago.

The Basic Problem

Computers on the internet find each other using IP addresses - numbers like 142.250.185.78. But humans are terrible at remembering long numbers. We are much better with words.

DNS solves this by translating domain names (google.com) into IP addresses (142.250.185.78). It is essentially a massive, distributed phone book for the internet.

What Happens When You Visit a Website

Here is the simplified version of what happens when you type "example.com" in your browser:

1. Browser cache check: Your browser remembers recent lookups. If you visited this site recently, it already knows the IP address.
2. Operating system cache: If the browser does not know, it asks your operating system, which also keeps a cache.
3. Router cache: Your home router often caches DNS lookups too.
4. ISP DNS server: If nobody local knows, the query goes to your internet provider's DNS servers.
5. Recursive lookup: If your ISP does not know, it asks other DNS servers until it finds the answer.

This all happens in milliseconds, typically. You never notice it.

DNS Record Types

DNS does not just store IP addresses. Different record types serve different purposes:

Why DNS Matters for Performance

DNS lookup time adds to page load time. This is why:

• Browsers and operating systems cache aggressively
• Some people use faster public DNS servers (like 1.1.1.1 or 8.8.8.8)
• CDNs use DNS to route you to nearby servers
• DNS prefetching hints help browsers look up domains before you click

Common DNS Issues

Propagation delays: When you change DNS records, the old values are cached everywhere. It can take 24-48 hours for changes to fully propagate worldwide. This is not a bug - it is how caching works.

DNS not resolving: If a website works for some people but not others, DNS is often the culprit. Different ISPs cache differently, and sometimes old records stick around.

DNS poisoning/spoofing: Attackers can sometimes trick DNS servers into returning wrong IP addresses, sending you to malicious sites. DNSSEC helps prevent this.

Choosing a DNS Provider

Your ISP provides DNS by default, but you can use alternatives:

• 1.1.1.1 (Cloudflare): Fast, privacy-focused
• 8.8.8.8 (Google): Reliable, widely used
• 9.9.9.9 (Quad9): Blocks known malicious domains

Changing DNS is usually done in your router settings or your device's network configuration. It is a five-minute change that can improve both speed and privacy.

DNS for Website Owners

If you run a website, understanding DNS helps you:

• Set up email properly with MX records
• Point subdomains to different services
• Verify domain ownership for various services
• Understand why changes take time to propagate
• Troubleshoot "site not loading" issues

Most domain registrars provide DNS management. For more control, you can use dedicated DNS providers like Cloudflare DNS or AWS Route 53.

The Takeaway

DNS is infrastructure you use constantly but rarely think about. It is a remarkably elegant solution to a fundamental problem: helping computers find each other using human-readable names instead of numbers.

Next time a website loads, you will know what happened in those few milliseconds before any actual content arrived.